Composite torque rotating electric machine

ABSTRACT

A composite torque rotating electric machine includes a stator having armature windings arranged at multiple positions in a circumferential direction, a rotor having a cylindrical core, first permanent magnets arranged on axes (d) and in the circumferential direction on the outer periphery of the rotor, second permanent magnets arranged on axes (d) on the inner periphery side of the rotor across from the permanent magnets on the outer circumference side, third permanent magnets on axes (q) and extending in the longitudinally and radially of the rotor, and air gaps on the outer periphery side of the third permanent magnets and intermediate in the circumferential direction of the first permanent magnets. The radial distance between the first and second magnets is greater than the circumferential distance between the first permanent magnets and the air gaps. A rectifier having multiple slits is disposed between the first permanent magnets and the air gaps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is the U.S. National Phase of PCT/JP2012/063673 filedMay 28, 2012, the subject matter of which is incorporated herein byreference in entirety.

TECHNICAL FIELD

The present invention relates to a composite torque rotating electricmachine using permanent magnets having a low residual magnetic fluxdensity such as ferrite magnets.

BACKGROUND ART

In a synchronous motor in which permanent magnets are buried in a rotor,the magnetic pole central axis of each permanent magnet is referred toas a d-axis, and an axis that is electrically and magneticallyorthogonal to the d-axis is referred to as a q-axis. As a conventionalstructure, an example in which plural permanent magnets are buried inthe d-axis has been known (for example, see Patent Literature 1).Further, as a permanent magnet-type rotating electric machine combinedwith reluctance torque, Patent Literature 2 has been known. Further,Patent Literature 3 shows a rotor of a permanent magnet-type rotatingmachine whose configuration is simplified by reducing the number ofpermanent magnets while obtaining high reluctance torque.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 3290392

Patent Literature 2: Japanese Patent No. 3970392

Patent Literature 3: Japanese Patent Application Laid-Open No.2001-145283

SUMMARY OF INVENTION Technical Problem

A composite torque rotating electric machine realizes high torque bycombining reluctance torque of armature magnetic flux generated atarmature windings of a stator with magnet torque of magnet magnetic fluxof permanent magnets.

In a conventional structure shown in Patent Literature 1, pluralpermanent magnets are buried in the d-axis direction. However, due tothe structure in which the permanent magnets are buried, iron cores arepresent across the entire outer periphery of a rotor corresponding tothe outer periphery side of the permanent magnets, and the spatialharmonic of closed loop armature magnetic flux generated at armaturewindings of a stator easily flows in the iron core portions. The closedloop spatial harmonic hardly contributes to the reluctance torque.However, when the closed loop spatial harmonic passes through the ironcores of the stator and the rotor, the magnetic saturation trend of theiron cores is enhanced. As a result, the effective amount of magneticflux that contributes to the reluctance torque has not been sufficientlyobtained.

Further, in order to further enhance the reluctance effect, sectionsbetween the permanent magnets are largely opened so that the magneticflux can easily flow in from the one q-axis direction (Patent Literature1 and FIG. 2). Then, the magnetic flux flowing in from the one q-axisdirection passes through the inner periphery side of the permanentmagnets buried on the inner periphery side on the d-axis, and flows outfrom the other q-axis direction. However, a magnetic path of the routebecomes long, and thus the magnetoresistance is increased. Accordingly,a magnetic loss is disadvantageously increased.

Further, due to the necessity of spaces by largely opening the sectionsbetween the permanent magnets in the iron core portions in the q-axisdirection, it is difficult to form plural poles because of restrictionson the dimension and arrangement of the permanent magnets. Thus, thesize of the rotor needs to be increased for plural poles. Further,because the sections between the permanent magnets in the iron coreportions in the q-axis direction are largely opened, the dimension ofeach of the plural permanent magnets in the d-axis needs to be reduced,and the magnet torque cannot be sufficiently obtained.

The conventional structure of Patent Literature 2 is a representativestructure as a structure of the permanent magnet-type rotating electricmachine combined with the reluctance torque. The reluctance torque inthe structure is generated at the iron core portions on the outerperiphery side relative to the permanent magnets. In order to ease themagnetic saturation in the iron core portions, the permanent magnets arearranged nearer the inner periphery side to increase the dimension ofthe iron core portions. In this case, the length of each permanentmagnet in the circumferential direction of the rotor is shortened, andthe magnet torque is reduced.

In the rotating electric machine using the permanent magnets, neodymiummagnets are used particularly for the permanent magnets positioned onthe outer periphery side of the rotor in order to avoid an increase inmagnet torque and permanent demagnetization. However, it is verydifficult to obtain neodymium and dysprosium of rare-earth metal, andthey are very expensive. On the other hand, ferrite magnets can beeasily obtained, and are inexpensive. However, the magnet torque issmall due to a low magnetic force, and further the permanentdemagnetization easily occurs due to a low retaining force.

Patent Literature 3 shows a rotor of a permanent magnet-type rotatingmachine whose configuration is simplified by reducing the number ofpermanent magnets while obtaining high reluctance torque. However, themagnetic path of the magnetic flux from the stator passes throughbetween one end of the longitudinal direction of the permanent magnetpositioned on the outer periphery side and the permanent magnetpositioned in the radial direction, and runs through between the otherend of the longitudinal direction of the permanent magnet and theadjacent permanent magnet through the inside of a trapezoidal shape. Asdescribed above, the magnetic flux from the stator takes a shortcut inthe inside of the trapezoidal shape. Therefore, the magnetic flux islikely to be saturated at the iron core portions in the inside of thetrapezoidal shape, and the magnetoresistance is increased.

The present invention has been achieved in view of the above-describedproblems, and armature magnetic flux generated from armature windings ofa stator is rectified using rectifying units of plural slits to realizehigh torque of a composite torque rotating electric machine usingpermanent magnets having a low residual magnetic flux density such asferrite magnets.

Solution to Problem

In order to achieve the above-described object, the present inventionprovides a composite torque rotating electric machine including: astator in which armature windings are arranged at plural areas in thecircumferential direction at regular intervals; a rotor that isconfigured using a cylindrical iron core obtained by laminating magneticsteel sheets; plural first permanent magnets that are provided on d-axesand that are arranged in the circumferential direction on the outerperiphery of the rotor; plural second permanent magnets that areprovided on the d-axes and that are arranged on the inner periphery sideof the rotor to face the permanent magnets on the outer periphery side;third permanent magnets that are provided on q-axes and that areradially stretched in the longitudinal direction in the rotor; and airgap portions that are provided in the middle of the circumferentialdirection of the plural first permanent magnets on the outer peripheryside of the third permanent magnets, wherein the distances in the radialdirection between the first permanent magnets and the second permanentmagnets are larger than those in the circumferential direction betweenthe first permanent magnets and the air gap portions, and rectifyingunits configured using plural slits are provided between the firstpermanent magnets and the air gap portions.

Further, in the above-described composite torque rotating electricmachine, the intervals between the plural slits are longer on the innerperiphery side than those on the outer periphery side.

Further, in the above-described composite torque rotating electricmachine, a first slit of the plural slits near the first permanentmagnet is parallel to the q-axis, and a second slit nearest to theq-axis is parallel to the d-axis.

Further, in the above-described composite torque rotating electricmachine, slits provided between the first slit and the second slit aredivided at an intersection point as the center between the central axisof the first slit and the central axis of the second slit.

Further, in the above-described composite torque rotating electricmachine, slits provided between the first slit and the second slit aredivided into equal angles at an intersection point as the center betweenthe central axis of the first slit and the central axis of the secondslit.

Further, in the above-described composite torque rotating electricmachine, non-magnetic bodies are enclosed in the inside of the pluralslits.

Advantageous Effects of Invention

According to the present invention, high composite torque of reluctancetorque of armature magnetic flux and magnet torque of permanent magnetscan be realized in a permanent magnet rotating electric machine usingpermanent magnets having a low residual magnetic flux density such asferrite magnets.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a composite torque rotating electricmachine in the radial direction according to a first embodiment of thepresent invention.

FIG. 2 is an enlarged view of main parts of a rotor structure accordingto the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of arrangement of slits.

FIG. 4 is a conceptual diagram of spatial harmonics of armature magneticflux.

FIG. 5 is a conceptual diagram of the flow of the spatial harmonics inthe embodiment of the present invention.

FIG. 6 are diagrams each showing a positional relation between the rotorand teeth of a stator at an arbitrary angle in the embodiment of thepresent invention.

FIG. 7 is a diagram for showing the flow of magnetic flux of armaturewindings in the entire rotor.

FIG. 8 is a diagram for showing the flow of magnet magnetic flux ofpermanent magnets in the entire rotor.

FIG. 9 is a diagram for showing the distribution of magnetic flux by anelectromagnetic analysis according to the embodiment of the presentinvention.

FIG. 10 are diagrams for showing examples of models to be compared andstudied by the electromagnetic analysis.

FIG. 11 are diagrams for showing results by the electromagneticanalysis.

FIG. 12 is a cross-sectional view of a composite torque rotatingelectric machine in the radial direction according to a secondembodiment of the present invention.

FIG. 13 is an enlarged view of main parts of a rotor structure accordingto the second embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

In embodiments of the present invention, the respective effects obtainedfrom the following configurations (a) to (f) are considered.

(a) Permanent magnets to serve as magnetic flux blocking units thatblock the inflow and outflow of armature magnetic flux generated atarmature windings arranged at teeth of a stator are arranged on theouter periphery side on d-axes of a rotor.

(b) Permanent magnets having a rectangular shape to prevent shortcircuit of magnetic flux between adjacent magnetic poles and to serve asrectification of a magnetic path are arranged on the inner peripheryside.

(c) Permanent magnets serving to prevent short-circuit magnetic fluxwith adjacent magnetic poles are arranged on q-axes of the rotor.

(d) An air gap having a trapezoidal shape in which the inner peripheryside corresponds to a long side and the outer periphery side correspondsto a short side is arranged at an end on the outer periphery side ofeach of the permanent magnets.

(e) The interval between each permanent magnet positioned on the outerperiphery side on the d-axis of the rotor and each permanent magnet onthe q-axis and each air gap having a trapezoidal shape is provided widerso that magnetic flux from the stator easily flows in the rotor.(f) Rectifying units configured using plural slits are formed at an ironcore in an area where the interval is wide.

By employing each of the above-described configurations as necessary, arotating electric machine with high torque can be obtained. For example,permanent magnets are arranged so as to surround the edges of magneticpoles using the permanent magnets in the rotor, and thus more magnetmagnetic flux can be obtained. Accordingly, magnet torque can bemaximally used.

Further, the spatial harmonic of armature magnetic flux can be blockedin the entire circumferential area on the outer periphery side of theiron core in the rotor using each permanent magnet positioned on theouter periphery side on the d-axis of the rotor, each air gap having atrapezoidal shape positioned on the outer periphery side on the q-axis,and plural slits formed therebetween, and the magnetic saturation trendin the stator and the rotor can be suppressed. Thus, the amount ofmagnetic flux effective for torque can be amplified, and high torque canbe realized.

Further, in the case where high torque is realized using permanentmagnets having a low residual magnetic flux density such as ferritemagnets, it is necessary to use more reluctance torque. In the case of areluctance-type rotating electric machine, a magnetic density differenceis enlarged between the d-axis direction and the q-axis direction, sothat the reluctance torque can be increased. However, the torquepulsation per one cycle is generally increased by the magnetic densitydifference.

In the embodiments, the magnetic flux can be rectified by the slitgroups. Thus, the reluctance torque can be increased, and at the sametime, the torque pulsation can be suppressed. Further, the air gapspositioned at ends on the outer periphery side of the permanent magnetson the q-axis are formed in a trapezoidal shape, so that the magneticflux flowing in from the teeth of the stator can be rectified, and thusthe same effect as the above-described slit groups can be obtained.

Further, the magnetic flux passes through the iron core portion having alarge area surrounded by the permanent magnets positioned on the outerperiphery side and the inner periphery side on the d-axis and thepermanent magnets positioned on the q-axis. Thus, the magnetoresistancecan be reduced, a magnetic path of the magnetic flux can be shortened,and a magnetic loss can be decreased. Further, if the magnetic fluxpasses through the iron core portion, the restrictions on thearrangement of the permanent magnets along the q-axis and the thicknessin the circumferential direction can be eased. Thus, plural poles can beeasily formed.

Hereinafter, a detailed structure of each embodiment of the presentinvention will be described using the drawings. It should be noted thata permanent magnet has a low residual magnetic flux density in thedescription of each embodiment unless otherwise described. Specifically,the permanent magnet denotes a magnet referred to as a ferrite magnet.

First Embodiment

First, a structure of a first embodiment will be described using FIG. 1to FIG. 2. FIG. 1 is a cross-sectional view of a composite torquerotating electric machine in the radial direction, and FIG. 2 is anenlarged view of main parts of a rotor structure. It should be notedthat a d-axis (magnetic pole central axis of permanent magnets) and aq-axis that is electromagnetically orthogonal to the d-axis arerepresented by dashed-dotted lines in FIG. 2.

The composite torque rotating electric machine of the embodiment isconfigured using a stator 1 having octal armature windings, and acylindrical rotor 3. The iron core of the rotor 3 is configured usinglaminated circular magnetic steel sheets, and permanent magnets composedof three or more ferrite magnets are buried in one magnetic pole. Pluralteeth 4 are formed in the stator 1 across the inner circumferentialdirection, and armature windings 2 are wound and arranged around therespective teeth 4.

A structure of the rotor 3 will be described using FIG. 2. Permanentmagnets 21 (first permanent magnets 21) in each of which thecircumferential direction corresponds to the longitudinal direction arearranged on the outer periphery side of the rotor 3. Each of thepermanent magnets 21 on the outer periphery side is buried in apermanent magnet insertion air gap portion 11 having nearly arectangular shape formed on the outer periphery side on the d-axis, andis fixed by adhesive material or rubber made of resin. Each of thepermanent magnets 21 is magnetized in the direction parallel to thed-axis. Further, the permanent magnet insertion air gap portion 11 isformed longer in the circumferential direction than each permanentmagnet 21, and air gaps 31 having nearly a triangular shape or nearly atrapezoidal shape are formed at both ends of each permanent magnet 21.

Further, permanent magnets 22 (third permanent magnets) are arranged inthe rotor 3 so as to be stretched along the q-axes. Each of thepermanent magnets 22 is buried in a permanent magnet insertion air gapportion 12 having nearly a rectangular shape formed on the q-axis, andis fixed by adhesive material or rubber made of resin. Each of thepermanent magnets 22 is magnetized in the direction orthogonal to theq-axis. In the case where the surface on the outer periphery side ofeach permanent magnet 21 corresponds to the north pole, each of thepermanent magnets 22 is arranged in such a manner that the surfacefacing the d-axis in which the permanent magnet 21 is buried correspondsto the north pole. On the contrary, in the case where the surface on theouter periphery side of each permanent magnet 21 corresponds to thesouth pole, each of the permanent magnets 22 is arranged in such amanner that the surface facing the d-axis in which the permanent magnet21 is buried corresponds to the south pole. An air gap 42 having atrapezoidal shape is formed at an end on the outer periphery side ofeach permanent magnet 22, and air gaps 32 having a triangular shape or atrapezoidal shape are formed at an end on the inner periphery side.

Further, permanent magnets 23 (second permanent magnets) in each ofwhich the circumferential direction corresponds to the longitudinaldirection are arranged in the rotor 3 on the inner periphery siderelative to the permanent magnets 21. Each of the permanent magnets 23on the inner periphery side is buried in a permanent magnet insertionair gap portion 13 having a rectangular shape formed on the innerperiphery side on the d-axis, and is fixed by adhesive material orrubber made of resin. Each of the permanent magnets 23 is magnetized inthe direction parallel to the d-axis. In the case where the surface onthe outer periphery side of each permanent magnet 21 corresponds to thenorth pole, each of the permanent magnets 23 is arranged in such amanner that the surface on the outer periphery side corresponds to thenorth pole. In the case where the surface on the outer periphery side ofeach permanent magnet 21 corresponds to the south pole, each of thepermanent magnets 23 is arranged in such a manner that the surface onthe outer periphery side corresponds to the south pole.

With the above-described arrangement, the permanent magnets 21 to 23 arearranged to be positioned on the respective sides of a trapezoid on therotor 3. An interval A between the permanent magnet 21 positioned on theouter periphery side on the d-axis of the rotor and the permanent magnet22 and the air gap 42 having a trapezoidal shape on the q-axis is set ata length where armature magnetic flux from the stator easily flows in.When the distance between the permanent magnets 21 and 23 is B, thedistance B is set larger than the distance A, and the armature magneticflux from the stator 1 can easily flow in. It should be noted that Adenotes a distance in the circumferential direction between the firstpermanent magnet and the air gap portion, and B denotes a distance inthe radial direction between the first permanent magnet and the secondpermanent magnet.

It should be noted that an example of the magnetization direction ofeach of the permanent magnets 21 to 23 is illustrated in FIG. 2.Specifically, the permanent magnets 21 and the permanent magnets 23 aremagnetized in such a manner that each outer periphery side correspondsto the north pole and each inner periphery side corresponds to the southpole in the embodiment, and the permanent magnets 22 are magnetized insuch a manner that the north poles face each other.

A slit group (slit portion) 51 is configured using plural slits 51 a to51 d at an iron core portion between the air gap 42 having a trapezoidalshape positioned on the outer periphery side of each permanent magnet 22and each permanent magnet 21. Four slits are shown in the embodiment,but the number thereof is not limited to four. The air gaps 42 having atrapezoidal shape and the slit groups 51 are non-magnetic bodies(non-magnetic body portions), and configure magnetic flux blocking unitstogether with the permanent magnets 21.

Each of the slit groups 51 is arranged on the outer periphery side ofthe rotor 3. More preferably, each of the slit groups 51 is formed onthe outer periphery side relative to a straight line connecting a corneron the inner periphery side of each permanent magnet 21 to the center ofa side on the outer periphery side of each air gap 42 having atrapezoidal shape. Each of the slits 51 a to 51 d configuring the slitgroups 51 is thin in width in the circumferential direction of the rotor3, and is formed in an elongated shape stretching in the radialdirection. Plural slit groups are provided in the circumferentialdirection at intervals. These slits 51 a to 51 d may be arrangedparallel to each other. Preferably, these slits 51 a to 51 d areradially arranged in such a manner that the intervals between the slitsare narrower on the outer periphery side and are wider on the innerperiphery side.

More preferably, the slit group 51 is radially arranged as shown in FIG.3. Specifically, the first slit 51 a nearest to the permanent magnet 21is formed to be parallel to the q-axis, and the second slit 51 d nearestto the q-axis is formed to be parallel to the d-axis. The first andsecond slits 51 b and 51 c are radially arranged in such a manner thatan angle having an intersection point 55 as the center between thecentral axis of the first slit 51 a and the central axis of the secondslit 51 d is divided into nearly equal angles.

Further, the lengths of the respective slits are shortened at a constantrate from the d-axis side toward the q-axis side. Specifically, the slit51 a is the longest slit, and the slit 51 d is the shortest slit. Theslits 51 b and 51 c therebetween are formed shorter in order. The slitgroup 51 is formed nearly in the middle in the circumferential directionbetween each permanent magnet 21 and each air gap 42 having atrapezoidal shape. Non-magnetic bodies such as air and resin areenclosed in the inside of each slit, and the enclosure of thenon-magnetic bodies can enhance the strength of the iron core.

With the above-described structure employed, the following effects canbe expected. The first effect is obtained by the structure at the outerperiphery portion of the rotor 3. In the embodiment, the permanentmagnets 21 are arranged on the outer periphery side of the rotor, andthe air gaps 31 are provided at both ends in the longitudinal directionof each permanent magnet 21. In addition, the slit groups 51 are presentadjacent to the air gaps 31, and further the air gaps 42 are presentadjacent to the slit groups 51. Next, the slit group 51, the air gap 31,and the permanent magnet 21 are repeatedly present across the entirecircumferential direction. Therefore, it is possible to obtain an effectin which closed loop spatial harmonics (magnetic flux) generated at theteeth 4 around the stator windings 2 can be blocked by the structure atthe outer periphery portion of the rotor 3.

The second effect is obtained as a rectifying unit (guiding unit) by theslit group 51 for the armature magnetic flux generated by the statorwindings 2. Specifically, the slits are radially arranged in such amanner that the intervals between the slits are narrower on the outerperiphery side and are wider on the inner periphery side. Accordingly,when the magnetic flux passes through each slit group 51, the magneticflux is rectified and guided to be radially expanded. Then, the magneticflux flows while being entirely diffused in an iron core portion 72having a large area sandwiched between each permanent magnet 21 and eachpermanent magnet 23. Further, the slit 51 a is formed to be the longestslit. Thus, the magnetic flux passing through the iron cores on the bothsides of the slit is guided farther in the direction along the slit 51a. Accordingly, the magnetic flux is guided so as to be entirelydiffused without shortcut in the iron core portion 72.

Hereinafter, these two effects will be described using the drawings.

FIG. 4 shows a conceptual diagram of the spatial harmonics of thearmature magnetic flux. When current is applied to the armature windings2, the closed loop armature magnetic flux is generated around thearmature windings 2. The armature magnetic flux includes magnetic fluxforming a closed loop of one slot that flows in the rotor 3 from oneteeth of the stator 1 and that flows in from the other nearest teeth.The magnetic flux is the spatial harmonic 61 of the armature magneticflux, and is different in cycle from the output torque. Thus, thespatial harmonic 61 does not contribute to the output torque. However,the magnetic flux is present in the iron core, and thus the magneticsaturation trend in the iron core portions of the stator 1 and the rotor3 is enhanced. Specifically, the spatial harmonic 61 does not contributeto the rotation of the electric machine at all, but causes the magneticsaturation. Thus, the effective amount of magnetic flux contributing tothe torque cannot be sufficiently obtained, and it is necessary tosuppress the spatial harmonic.

FIG. 4 does not show the structure of the embodiment, but shows a statein which the spatial harmonics 61 (shown by arrows of solid lines in thedrawing) of the armature magnetic flux are generated at plural areas.Further, the spatial harmonic (shown by an arrow 62 of a dotted line inthe drawing) generated around the armature windings 2 positioned in themiddle of FIG. 4 is blocked by the permanent magnet 21.

FIG. 5 shows a conceptual diagram of the flow of the spatial harmonic inthe embodiment. The spatial harmonic of the armature magnetic fluxeasily passes through a magnetic body such as an iron core. However, ifa non-magnetic body such as air or resin is provided on a magnetic paththrough which the spatial harmonic passes, the spatial harmonic isblocked by the non-magnetic body. In the embodiment, the spatialharmonic is blocked by arranging the permanent magnets 21, the slitgroups 51, and the air gaps 42 having a trapezoidal shape on the outerperiphery side of the rotor.

Further, the spatial harmonic configures a closed loop at the adjacentteeth as described above. Therefore, the intervals between the permanentmagnets 21 and the air gaps 42 having a trapezoidal shape, the intervalsbetween the permanent magnets 21 and the slit groups 51, the intervalsbetween the slit groups 51 and the air gaps 42 having a trapezoidalshape, and the intervals between the slits are set narrower than theadjacent teen intervals (teeth pitches) of the stator 1. Thus, thespatial harmonic 61 can be effectively blocked. In other words, thespatial harmonic can be blocked by arranging the permanent magnetsarranged on the outer periphery side of the rotor 3, or the non-magneticbodies (the air gaps 31, the air gaps 42, and the slits 51 a to 51 d inthe embodiment) such as the air gaps in the following manner.

The distance between each permanent magnet and each non-magnetic bodyportion, the distance between each permanent magnet and each slitportion, the distance between each slit portion and each air gap, andthe distance Xn (in this case, Xn represents the n-th distance and anexample in which the largest number of n is 6 is shown in the drawing)between the slits are set smaller (Xn<Y) than the interval Y (Y is usedbecause the intervals between the teeth are constant) between the teeth4 of the stator 1. With such a configuration, the spatial harmonic ofthe armature magnetic flux always passes through the permanent magnetsor the non-magnetic bodies. Thus, the spatial harmonic can be reliablyblocked and suppressed.

FIGS. 6(a) to (c) show positional relations between the rotor 3 and theteeth 4 of the stator at an arbitrary angle. As described above, theinterval Xn is set narrower than, at least, the interval Y between theteeth. Accordingly, if the positional relations between the teeth of thestator and the rotor are changed during the operation, the spatialharmonic can be blocked at any position on the magnetic path of thespatial harmonic because the permanent magnets 21, the slit groups 51,and the air gaps 42 having a trapezoidal shape are present.

Specifically, the permanent magnets 21, the air gaps 42, and the slitgroups 51 are arranged in order in the circumferential direction on theouter periphery side of the rotor, and realize the effect of suppressingthe spatial harmonic that does not contribute to the torque and that isgenerated around the armature windings. The permanent magnet portions,the air gap portions, and the slit portions (slit groups) function asthe magnetic flux blocking portions, and extend in the circumferentialdirection, so that unnecessary magnetic flux is cut. As shown by dottedlines 62 in FIGS. 6(a) to (c), it is apparent that the spatial harmonicis effectively blocked irrespective of the rotational position of therotor 3.

The flow of the armature magnetic flux in the rotor of the electricmachine will be described using FIG. 7. FIG. 7 is a diagram for showingthe flow (arrows of solid lines) of the armature magnetic flux in theentire rotor 3 in the embodiment. The inflow and outflow in the d-axisdirections of the armature magnetic flux generated from the armaturewindings 2 of the stator 1 are blocked by the permanent magnets 21. Onthe other hand, the armature magnetic flux in the q-axis directions isdivided by the air gaps 42 having a trapezoidal shape and the permanentmagnets 22 to flow in the rotor 3. Specifically, the armature magneticflux flows in from the outer periphery side of the slit group 51, passesthrough the iron core portion 72 having a large area sandwiched betweenthe permanent magnet 21 and the permanent magnet 23, and flows out fromthe outer periphery side of the other slit group 51. As described above,the armature magnetic flux is allowed to flow in while being divided.Accordingly, the armature magnetic flux passing through the iron coreportion 72 having a large area sandwiched between the permanent magnet21 and the permanent magnet 23 can be increased without magneticsaturation. In addition, the magnetoresistance can be reduced, and thereluctance torque can be increased.

Next, the magnetic flux of the permanent magnets will be described. FIG.8 is a diagram for showing the flow of the magnet magnetic flux of thepermanent magnets. The magnetization direction of each permanent magnet21 positioned on the outer periphery side on the d-axis is arranged toface the armature magnetic flux, so that the gap of magnetic density isenlarged and the saliency is increased. Thus, the reluctance torque canbe increased. Further, the magnetic poles of the permanent magnets 22and 23 are allowed to face each other, and thus the magnet magnetic fluxis converged. Accordingly, the magnet torque can be increased.

FIG. 9 is a diagram for showing the distribution of magnetic flux by anelectromagnetic analysis of the embodiment, and is a conceptual diagramfor explaining the effect of the above-described slit groups 51. Inorder to realize a high output by actively using the reluctance torque,the slit groups 51 are provided in the embodiment as described above(see FIG. 1 to FIG. 2). It can be confirmed that each of the slit groups51 has the effect of a rectifying unit (guiding unit) that rectifies andguides the flow of the magnetic flux that flows in or out between therotor 3 and the stator 1.

In general, the magnetic flux is concentrated on the inner peripheryside to forma short loop, and thus the magnetic saturation trend at theiron core portion on the inner periphery side is generally enhanced. Theslit intervals on the inner periphery side are wider than those on theouter periphery side in the embodiment, so that the magnetic flux isrectified to the flow diffused in the entire iron core portion 72sandwiched between the permanent magnet 21 and the permanent magnet 23by the slit group 51. When the magnetic flux flows in the rotor 3 fromthe stator 1, the magnetic flux is divided by the air gaps 42 having atrapezoidal shape and the permanent magnets 22. Each divided magneticflux 70 passes through the slit group 51, and is radially expanded to bediffused in the entire iron core portion 72 that is widely formed in therotor 3. Accordingly, the magnetic saturation trend can be suppressed atthe iron core portion 72, and the magnetoresistance can beadvantageously reduced as the entire rotor. The magnetic flux 71diffused by the slit group 51 passes through the other slit group 51 andflows out from the rotor. However, the magnetic flux diffused whenpassing through one slit group 51 is rectified and aggregated by theother slit group 51. Thus, the saliency is not deteriorated.

As shown in FIG. 9, while the distance B between the permanent magnet 21and the permanent magnet 23 is large and the iron core portion 72serving as the flow path of the magnetic flux is widely formed, theinflow and outflow side of the magnetic flux, namely, the distance Abetween an end of the permanent magnet 21 and the air gap 42 having atrapezoidal shape is shorter than the distance B between the permanentmagnet 21 and the permanent magnet 23. Thus, when the magnetic fluxflows in, the magnetic flux flows from a narrow portion to a wideportion of the slit group 51 to be diffused. When the magnetic fluxflows out, the magnetic flux is aggregated. Accordingly, the flow of themagnetic flux can be effectively rectified (regarding the distance A andthe distance B, see FIG. 2). Further, in addition to the above, the flowof the magnetic flux can be more effectively rectified by the rectifyingeffect of the magnetic flux by the slit group 51.

As the verification of the rectifying effect of the magnetic flux, anelectromagnetic analysis was made for three examples. The structures andresults of each example will be described below.

FIG. 10 are diagrams each showing an example of a model to be comparedand studied by the electromagnetic analysis. A case 1 of FIG. 10(a)shows the above-described structure of the embodiment. A case 2 of FIG.10(b) shows an example in which the all slits formed between thepermanent magnet 21 and the air gaps 42 having a trapezoidal shape areformed parallel to the q-axis, and the lengths thereof in the radialdirection are the same. A case 3 of FIG. 10(c) shows a comparisonexample in which no slit groups 51 are provided and air gaps 43 on theouter periphery side of the permanent magnets 22 are formed in arectangular shape.

FIG. 11(a) shows a determination table of average output torque andtorque pulsation by the electromagnetic analysis in each case of FIG.10, and FIGS. 11(b) to (d) show torque waveforms thereof. The averageoutput torque was sufficiently obtained in the case 1 and the case 2.However, the average output torque in the case 3 was decreased by about5% as compared to the case 1 or the case 2.

The torque pulsation in the case 1 is about 5% which is the mostexcellent, and that in the case 2 is 10% or less. The torque pulsationin the case 3 is 20% or more. In consideration of the fact that thetorque pulsation is generally about 20% in the reluctance-type rotatingelectric machine using the reluctance torque, it is apparent that theslit groups 51 and the air gaps 42 having a trapezoidal shape formed inthe case 1 and the case 2 are considerably effective.

As described above, the permanent magnets 21, the slit groups 51, andthe air gaps 42 having a trapezoidal shape are provided to contribute tothe suppression of the spatial harmonic, and the magnetic flux flowingin the circumferential direction can be effectively cut by theconfigurations (see FIG. 4 to FIG. 6). On the other hand, the shape ofintending to rectify the magnetic flux flowing into the rotor iron coreis effective (see FIG. 8 to FIG. 10), and thus the respective slits ofthe embodiment are desirably configured as follows.

(1) Stretch long in the direction along the radial direction

(2) Arrange to be expanded from the outer periphery side of the rotortoward the inner periphery side

In the structure of (1), a significant contribution to the rectifyingeffect of the magnetic flux can be confirmed (see the case 1 and thecase 2 of FIG. 10 and FIG. 11), and the effect of reducing the torquepulsation can be sufficiently obtained. Further, by arranging the slitsas in (2), the torque pulsation can be further reduced (see the case 1of FIG. 10 and FIG. 11), and a more preferred configuration can berealized.

The followings are summarized advantages of the structure in theembodiment. High torque using the permanent magnets having a lowresidual magnetic flux density can be realized by effectively using bothof the reluctance torque generated from the armature current and themagnet torque from the permanent magnets having a low residual magneticflux density such as ferrite magnets.

Specifically, the permanent magnets are buried on the outer peripheryside on the d-axes, the permanent magnets are formed on the q-axes, theair gaps having a trapezoidal shape are formed at the ends on the outerperiphery side thereof, the slit groups are formed between the permanentmagnets on the outer periphery side on the d-axes and the air gapshaving a trapezoidal shape, and the intervals in the circumferentialdirection are arranged narrower than the distances between the adjacentteeth of the stator. Accordingly, the spatial harmonic of the armaturemagnetic flux that does not contribute to the output torque can beblocked, and the magnetic saturation in the iron core portions of thestator and the rotor can be suppressed. Namely, the amount of magneticflux contributing to the output torque can be amplified, and thus theoutput torque can be increased.

Further, the magnetic flux is divided by the permanent magnets on theq-axes and the air gaps having a trapezoidal shape, and thus themagnetic saturation in the iron core portion of the rotor can be eased.Namely, the amount of magnetic flux contributing to the output torquecan be amplified, and thus the output torque can be increased, assimilar to the above.

Further, the slit groups that are expanded from the outer periphery sideof the rotor to the inner periphery side and that are shortened inlength from the d-axis toward the q-axis at a constant rate areprovided, so that the torque pulsation increased when using thereluctance torque can be significantly suppressed.

Second Embodiment

Next, an example different from the embodiment will be described. FIG.12 is a cross-sectional view of a composite torque rotating electricmachine in the radial direction according to a second embodiment of thepresent invention, and FIG. 13 is an enlarged view of main parts. Thecomposite torque rotating electric machine shown in each of FIG. 12 andFIG. 13 is configured using a stator 1 having octal armature windingsand a cylindrical rotor 3. An iron core of the rotor 3 of the structurein the embodiment is configured using laminated circular magnetic steelsheets, and three or more permanent magnets are buried in one magneticpole. Instead of the permanent magnets 21 of the first embodiment, slitgroups 52 are provided.

Each of permanent magnets 22 is buried in an air gap 12 having arectangular shape on a q-axis, and is fixed by adhesive material orrubber made of resin. Air gaps 42 having a trapezoidal shape are formedat ends on the outer periphery side of the permanent magnets 22. Airgaps 32 having nearly a triangular shape or nearly a trapezoidal shapeare provided at ends on the inner periphery side.

Each of permanent magnets 23 is buried in an air gap 13 having arectangular shape on the inner periphery side on a d-axis, and is fixedby adhesive material or rubber made of resin. Each of the permanentmagnets 23 is magnetized in the direction parallel to the d-axis. In thecase where the surface of each permanent magnet 22 facing the d-axiscorresponds to the north pole, each permanent magnet 23 is arranged insuch a manner that the surface on the outer periphery side correspondsto the north pole. In the case where the surface of each permanentmagnet 22 facing the d-axis corresponds to the south pole, eachpermanent magnet 23 is arranged in such a manner that the surface on theouter periphery side corresponds to the south pole.

Slit groups 51 of plural slits are formed at iron core portions betweenthe slit groups 52 and the air gaps 42 having a trapezoidal shapepositioned on the outer periphery side of the permanent magnets 22. Inthe second embodiment, four slits are shown as similar to the firstembodiment. However, it is apparent that the number of slits is notlimited to four.

A slit 51 a nearest to the slit group 52 is formed to be parallel to theq-axis (adjacent q-axis), and a slit 51 d nearest to the q-axis isformed to be parallel to the d-axis. Slits 51 b and 51 c have nearlyequal angles obtained by dividing an angle having an intersection pointas the center between the central axis of the slit 51 a and the centralaxis of the slit 51 d (see FIG. 3). The lengths of the respective slitsin the slit groups 51 are shortened from the d-axis side toward theq-axis side at a constant rate. The position in the circumferentialdirection of each slit group 51 is formed substantially in the middlebetween the slit group 52 and the trapezoidal air gap 42. Non-magneticbodies such as air and resin are enclosed in the inside of each slit.

Each of the slit groups 52 formed on the outer diameter side on thed-axes is configured using plural parallel slits, configures a magneticblocking unit as similar to the permanent magnets 21 of the firstembodiment, functions to block spatial harmonics 61 of armature magneticflux generated from armature windings 2 of the stator 1, and the sameeffect similar to the structure shown in the first embodiment can beobtained.

LIST OF REFERENCE SIGNS

-   1: stator, 2: armature winding, 3: rotor, 4: teeth, 11: permanent    magnet insertion air gap portion, 12: permanent magnet insertion air    gap portion, 13: permanent magnet insertion air gap portion, 21:    first permanent magnet, 21, 42, 51, 52: magnetic blocking unit, 22:    third permanent magnet, 23: second permanent magnet, 31, 32, 33: air    gap, 42: air gap having trapezoidal shape, 51: first slit, 51 d:    second slit, 52: slit group, 61: spatial harmonic of armature    magnetic flux, 62: blocked spatial harmonic of armature magnetic    flux, 72: iron core portion, A: distance in circumferential    direction between first permanent magnet and air gap portion, B:    distance in radial direction between first permanent magnet and    second permanent magnet Xn: distance between permanent magnet and    non-magnetic body portion, distance between permanent magnet and    slit portion, distance between slit portion and air gap, distance    between slits, Y: teeth interval (distance between teeth)

The invention claimed is:
 1. A composite torque rotating electricmachine comprising: a stator in which armature windings are arranged atplural areas in the circumferential direction at regular intervals; arotor that is configured using a cylindrical iron core obtained bylaminating magnetic steel sheets; plural first permanent magnets thatare provided on d-axes and that are arranged in the circumferentialdirection on the outer periphery of the rotor; plural second permanentmagnets that are provided on the d-axes and that are arranged on theinner periphery side of the rotor to face the first permanent magnets onthe outer periphery side; third permanent magnets that are provided onq-axes and that are stretched longitudinally in the radial direction inthe rotor; and air gap portions that are provided at a middle positionbetween the plural first permanent magnets along the circumferentialdirection on the outer periphery side of the third permanent magnets,wherein the distances in the radial direction between the firstpermanent magnets and the second permanent magnets are larger than thedistances in the circumferential direction between the first permanentmagnets and the air gap portions, and rectifying units configured usingplural slits are provided between the first permanent magnets and theair gap portions, a slit nearest the first permanent magnet has agreatest length of the plural slits, and only one second permanentmagnet is provided between two adjacent third permanent magnets.
 2. Thecomposite torque rotating electric machine according to claim 1, whereinthe intervals between the plural slits are longer on the inner peripheryside than those on the outer periphery side.
 3. The composite torquerotating electric machine according to claim 2, wherein a first slit ofthe plural slits near the first permanent magnet is parallel to theq-axis, and a second slit nearest to the q-axis is parallel to thed-axis.
 4. The composite torque rotating electric machine according toclaim 3, wherein slits provided between the first slit and the secondslit are evenly positioned with respect to an intersection point of thecentral axis in the longitudinal direction of the first slit and thecentral axis in the longitudinal direction of the second slit.
 5. Thecomposite torque rotating electric machine according to claim 1, whereinnon-magnetic bodies are enclosed in the inside of the plural slits. 6.The composite torque rotating electric machine according to claim 1,wherein the plural slits are arranged expanding toward the center of therotor.
 7. The composite torque rotating electric machine according toclaim 6, wherein slits provided between the first slit and the secondslit are divided into equal angles at an intersection point as thecenter between the central axis in the longitudinal direction of thefirst slit and the central axis in the longitudinal direction of thesecond slit.
 8. The composite torque rotating electric machine accordingto claim 1, wherein the plural slits are extended in the radialdirection along the magnetic flux passing between the q-axis and thed-axis.